The present invention relates generally to combination full flow and bypass filters.
A “clean” full-flow is advantageous for maintaining easy oil throughput during normal engine operation and especially during cold starts. A restricted full-flow impedes the flow of oil during a cold start. Consequently, there is an increase in the time to get oil to critical engine components and/or an excessive time that the filter bypass valve is open. Both situations (time delays and open bypass valves) are detrimental to engine health.
Prior to the development of combination full flow and bypass filters, engines generally employed one of two forms of filtration to clean the lubricating oil. One method is full-flow filtration and the other is combined full-flow and bypass filtration. Full-flow filtering elements receive and filter 90 to 100% of the regulated oil pump output prior to supplying the oil to the engine's lubrication system. Due to the need to filter a relatively high flow rate of oil, the full-flow filter is typically designed using more porous media than bypass filters. The higher porosity allows high oil throughput while yielding a desirably low pressure drop. Thus, the full-flow provides continuous engine protection by constantly removing relatively large particles.
Full flow filters are frequently augmented with bypass filters. Bypass filters, as indicated by their name, are placed in a flow path that bypasses the engine's main oil lubrication system. Typical bypass filters receive only five to ten percent of the regulated pump output, and serve to “superclean” the oil. “Supercleaning” is accomplished by use of a relatively low porosity media. To force oil through this tight media, high pressure oil is supplied to the bypass filter inlet while the filter's outlet is essentially at zero pressure (exit flow is routed to the non-pressurized oil pan). Hence, a high pressure differential drives the flow through the bypass filter. Since the bypass flow is pumped expressly for filtration and does not directly flow to the engine's main lubrication system, it is a parasitic pumping loss. To limit the amount of the parasitic bypass flow, a restrictive orifice is generally inserted between the bypass filter and the oil pan.
Of the two filtration systems discussed, the combination system (both full-flow and bypass filtration) provides the most engine protection, yet it is likely to be more costly than a full-flow system alone. Therefore, the Venturi Combo Lube Filter (VCLF) design was intended to provide the benefits of the combination filtration system while minimizing costs and complexity. The objective was to put the total filtration system in a single container and eliminate the additional plumbing associated with bypass filters.
Both full-flow filter media (FFM) and bypass type filter media (BPM) are preferably in a single container. A key feature of the Venturi Combo Lube Filter design is the increased utilization of the high capacity, high efficiency bypass type filter media. Specifically, the intent is to capture the bulk of the contaminant in the bypass type filter media while allowing the full-flow filter media to remain relatively clean. Thus, the full-flow filter media can provide continuous low-pressure-drop filtration.
The operation of the Venturi Combo Lube Filter is as follows; similar to the combination lube filter, the full-flow filter media and bypass type filter media share a common inlet. However, the Venturi Combo Lube Filter employs a venturi nozzle (see, for example, U.S. Pat. No. 5,695,637 to Jiang et al.) to direct and force/pull oil through the bypass type filter media at a high flow rate. The higher flow rate is accomplished via these flow mechanisms; the flow through the freer-flowing full-flow element is restricted by the nozzle throat at nozzle inlet, forcing more flow through the bypass type media. A low pressure zone in the throat of the nozzle generates a suction at the outlet of the bypass media, pulling more flow through the tight bypass section.
The bypass type filter media and full-flow filter media flows then merge inside the filter, thereby sending 100% of the filtered flow to the engine's lubrication system. The system is made energy efficient by the use of a nozzle diffuser which reduces the fluid's velocity to recover a portion of the pressure drop lost in the nozzle throat (ref. Bernoulli's equation).
Note the Venturi Combo Lube Filter preferably has only one outlet versus two in the combination lube filter. The single outlet simplifies engine plumbing. Also, elimination of the companion engine bypass flow circuit eliminates parasitic bypass flow. Having one filter inlet and outlet means existing applications which use full-flow-only filter can easily apply the Venturi Combo Lube Filter with no equipment/engine modifications.